LIMA Graft Not Ligated: Clinical Implications
When a LIMA graft is "not ligated," this typically refers to unligated side branches of the LIMA that remain patent after CABG, which can cause a coronary steal phenomenon leading to myocardial ischemia in the LAD distribution despite a patent LIMA-to-LAD graft. 1
Understanding the Problem
The LIMA is harvested during CABG and anastomosed to the LAD artery. During this process:
- Large LIMA side branches should typically be ligated during surgery to prevent competitive flow and steal phenomena 1
- When side branches remain unligated and patent, blood can preferentially flow through these lower-resistance pathways rather than through the distal anastomosis to the LAD 1
- This creates a "coronary steal" where blood is diverted away from the myocardium that needs revascularization 1
Clinical Consequences
Symptomatic Presentation
- Patients may develop angina in the LAD distribution despite having a technically patent LIMA-to-LAD graft 1
- Objective measures of LAD ischemia (stress testing, perfusion imaging) may demonstrate persistent ischemia 1
- This represents a technical complication of CABG that can compromise the intended revascularization 2
Mechanism of Ischemia
The unligated side branch acts as a low-resistance pathway that "steals" blood flow that should be directed to the coronary circulation. The blood follows the path of least resistance through the side branch rather than perfusing the ischemic myocardium distal to the LAD stenosis.
Management Approach
When coronary steal from an unligated LIMA side branch is identified as the cause of post-CABG angina, percutaneous embolization of the side branch is the treatment of choice: 1
- Coil embolization of the offending side branch can be performed percutaneously 1
- This intervention often results in improvement of anginal symptoms 1
- Objective measures of LAD ischemia frequently resolve after side branch occlusion 1
Diagnostic Considerations
When evaluating post-CABG patients with recurrent angina:
- Maintain a low threshold for angiography in post-CABG patients presenting with ischemia, as there are multiple potential anatomic culprits 3
- Angiography should specifically evaluate LIMA graft patency, the anastomosis site, and identify any patent side branches 1
- Visual examination alone may be insufficient to determine graft functionality—angiographic assessment is essential 4
Important Caveats
The controversy surrounding routine ligation of all LIMA side branches persists, but advocates for occlusion clearly demonstrate that in cases of LAD ischemia with identified patent side branches, treatment improves outcomes. 1 This is distinct from other CABG complications such as inadvertent anastomosis to cardiac veins, which represents a different technical error. 5